I recently installed two COMPLETELY identical Ubuntu 12.04 systems, PC01 and PC02. The browser is latest version of Mozilla Firefox. When visiting https://www.komplett.dk/k/signin.aspx with PC01, the connection is secure and everything is OK, no error messages. When visiting the same URL with PC02, the following error message is shown: --- This Connection is Untrusted You have asked Firefox to connect securely to www.komplett.dk, but we can't confirm that your connection is secure. Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified. What Should I Do? If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue. Get me out of here! Technical Details www.komplett.dk uses an invalid security certificate. The certificate is not trusted because no issuer chain was provided. (Error code: sec_error_unknown_issuer) I understand the Risks --- Why is this happening when the systems are COMPLETLY identical? i have tried to delete the profile folder on both systems, but the result is the same. NO certificates has been manually installed on PC01, so that is not the reason. The file size of cert8.db on PC01 is 94K and on PC02 it is 64K, I do not understand how the size can be different when the profiles are newly created. I would really like to find out why I am experiencing different behaviour with Firefox, on two identical systems, so any suggestions or ideas are very welcome.